This invention relates to the reciprocating folders used in packaging machines for folding an edge of a sheet or slip of wrapping material on one side fo an article to be packaged, and that consist of a blade, a fin, or the like, which is substantially flat and is movable parallelly and close to the article side on which the edge of the sheet or slip must be folded.
In the reciprocating folders of this kind, the edge of the wrapping sheet or slip is folded on the article to be packaged by means of the so-called forward or outward stroke of the reciprocating folder, after which the folder performs its return stroke into starting position, while the folded edge must remain in folded position on the respective side of the article to be packaged. However, during the return stroke of the folder, the folded edge is apt to be dragged along by the folder and to be retracted therewith owing to friction and/or the attraction due to statical electricity, the more so when the wrapping sheet or slip is of flabby material, i.e., not much rigid and/or easily chargeable with statical electricity, such as plastic material, particularly polyethylene.
The invention aims to eliminate the said drawback and, to this end, it provides one or more blowing nozzles which are so arranged and oriented that an air layer is generated between the folder and the folded edge of the sheet or slip, during the return stroke of said folder. Preferably, the blowing nozzle or nozzles are so oriented that their air jets are directed in opposite direction to the return stroke of the reciprocating folder.
The blowing nozzle or nozzles according to the invention can be located and arranged in any suitable manner. According to one embodiment of the invention, the blowing nozzle or nozzles can be provided in a fixed nozzle-carrying member which is substantially parallel to the folder and is located substantially on the ideal prolongation of that side of the article to be packaged on which the edge of the sheet is folded by the folder. According to another embodiment of the invention, the blowing nozzle or nozzles can be provided in the reciprocating folder itself.
The blowing nozzle or nozzles according to the invention can be intermittently activated, each time at the starting of, or shortly before the return stroke of the folder, or they can be continuously operated, especially when their jets are directed in the opposite direction to the return stroke of the folder.
In any case, the air layer which according to the invention is generated by means of the blowing nozzle or nozzles between the folder and the edge of the sheet folded on the article to be packaged, prevents this edge from being dragged along by the folder owing to friction and/or statical electricity, during the return stroke of the folder. At the same time, the air jets generated by the blowing nozzle or nozzles keep the folded edge tightly adherent to the respective side of the article to be packaged.